Thank you for the answer.
No, it was not an infection nor a malfunction. And even that, I still need a solution, because cleaning the computer does not bring back the tabs/sessions
I simply want to know how one can restore working sessions/tabs.
There is also a guide that uses some python commands to parse the content of s* and t* files and output the addresses, one by one, into a TXT file - then one has to take each line from that file, copy the address, create a new tab/window, paste the copied address, repeat
da capo. I can do it by hand, without the need for yet another programming medium on my computer.
I hoped for an automatic solution, like Menu->Tools->Advanced->Import Tabs